bsearch(3C)                    DG/UX R4.11MU05                   bsearch(3C)


NAME
       bsearch - binary search a sorted table

SYNOPSIS
       #include <stdlib.h>

       void *bsearch (const void *key, const void *base,
           size_t nel, size_t size,
           int (*compar)(const void *, const void *));

DESCRIPTION
       bsearch is a binary search routine generalized from Knuth (6.2.1)
       Algorithm B.  It returns a pointer into a table (an array) indicating
       where a datum may be found or a null pointer if the datum cannot be
       found.  The table must be previously sorted in increasing order
       according to a comparison function pointed to by compar.  key points
       to a datum instance to be sought in the table.  base points to the
       element at the base of the table.  nel is the number of elements in
       the table.  size is the number of bytes in each element.  The
       function pointed to by compar is called with two arguments that point
       to the elements being compared.  The function must return an integer
       less than, equal to, or greater than 0 as accordingly the first
       argument is to be considered less than, equal to, or greater than the
       second.


   Considerations for Threads Programming
                     +---------+-----------------------------+
                     |         |                      async- |
                     |function | reentrant   cancel   cancel |
                     |         |             point     safe  |
                     +---------+-----------------------------+
                     |bsearch  |     Y         N        N    |
                     +---------+-----------------------------+

EXAMPLE
       The example below searches a table containing pointers to nodes
       consisting of a string and its length.  The table is ordered
       alphabetically on the string in the node pointed to by each entry.

       This program reads in strings and either finds the corresponding node
       and prints out the string and its length, or prints an error message.

       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       struct node {                 /* these are stored in the table */
               char *string;
               int length;
       };
       static struct node table[] =  /* table to be searched */
       {
               { "asparagus", 10 },
               { "beans", 6 },
               { "tomato", 7 },
               { "watermelon", 11 },
       };

       main()
       {
               struct node *node_ptr, node;
               /* routine to compare 2 nodes */
               static int node_compare(const void *, const void *);
               char str_space[20];   /* space to read string into */

               node.string = str_space;
               while (scanf("%20s", node.string) != EOF) {
                       node_ptr = bsearch( &node,
                                  table, sizeof(table)/sizeof(struct node),
                                  sizeof(struct node), node_compare);
                       if (node_ptr != NULL) {
                               (void) printf("string = %20s, length = %d\n",
                                       node_ptr->string, node_ptr->length);
                       } else {
                               (void)printf("not found: %20s\n", node.string);
                       }
               }
               return(0);
       }

       /* routine to compare two nodes based on an  */
       /* alphabetical ordering of the string field */
       static int
       node_compare(const void *node1, const void *node2)
       {
               return (strcmp(
                               ((const struct node *)node1)->string,
                               ((const struct node *)node2)->string));
       }

DIAGNOSTICS
       A null pointer is returned if the key cannot be found in the table.

SEE ALSO
       reentrant(3), hsearch(3C), lsearch(3C), qsort(3C), tsearch(3C).

NOTES
       The pointers to the key and the element at the base of the table
       should be of type pointer-to-element.

       The comparison function need not compare every byte, so arbitrary
       data may be contained in the elements in addition to the values being
       compared.

       Although declared as type void *, the value returned should be cast
       into type pointer-element.

       If the number of elements in the table is less than the size reserved
       for the table, nel should be the lower number.


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